The production of multi-coated wires, i.e., those wires having a plurality of coats of insulating material, is produced by applying a plurality of coats of insulating material in layers onto a wire. Commonly, the individual coats of insulating material are applied by first passing the wire through an "enamel coating apparatus" and then the coat is dried by passing the wire through a high temperature "drying and curing" oven.
Typically, the ovens are tall, vertical free standing structures with walls made of stainless steel sheet metal and plates. One problem experienced is that the metal tends to buckle or bow inward, toward the direction of the wire, because of a large temperature gradient between the hot interior surface and the colder exterior surface. This tends to diminish the width of an already narrow wire passageway (work tube) oven and increases the probability of rubbing uncured enamel breaking or stripping the wires which are passing through the oven thereby degrading the product wire. With age this problem increases because with each heat-up the oven wall bows more toward the oven interior since there has been no force to restore the wall to its original position.
Typical solutions in the past have been to use long, slow heat-up times so as to hold the temperature gradient across the material low or a design of a heavy rigid frame with supports attached to the wall of the duct. However, the first solution, by its very nature, is very slow and time consuming and the second solution creates problems with thermal expansion of the duct.
Accordingly, what is needed in the art is a method which allows for quick heat-up of the oven while preventing the buckling of the oven wall toward the wire.